air pollution altitude ancient greek arithmetic automatic label placement cartographic relief depiction cartography charles hutton circle cloud color contour curve dew point economics edmond halley elevation english channel fathom france generalization gradient great britain groundwater hail humidity interpolation ireland isoclinic line isocost isogloss isoquant level set map mathematics merwede meteorology nautical chart noise health effects noise pollution oceanography ordnance survey phase diagram philippe buache pictometry pigment pressure russia sea level sheen slope snow soil contamination surface temperature terrain thermal pollution thermodynamic diagrams thermodynamics topographic map weather station wind